Tube drawing method



April 25, 1939. T. MCORE ET AL 2,155,437

TUBE DRAWING METHOD Filed Oct. 12, 195'? I 2g 2% INVENTORS, mw

TTORNEY.

Patented Apr. 25, 1939 UNITED STATES PATENT OFFICE 2,155,437 TUBEDRAWING METHOD Company of America,

Vania a corporation of Pennsyl- Application October 12, 1937, Serial No.168,572

4 Claims.

This invention relates to an improved method and means for drawingtubing, and particularly for drawing relatively long and relativelythinwalled metal tubing of relatively small diameter.

Broadly, it is an object of the present invention to provide an improvedmethod of and means for drawing material of the above describedcharacter. A more specific object is to provide means which can morereadily be brought into cooperative relationship with the tubing toeffect a reduction of gauge and thickness while maintaining a uniformoutside diameter over substantially the entire length of the tube.Another object is the provision of a method and means for maintaining afilm of lubricant within the interior of the tubing being drawn, tofacilitate subse-v quent drawing operations.

Other objects will. be apparent from the following description of theinvention .in tion with the drawing, in which:

Fig. 1 shows the tubing and the drawing tools prior to the beginning ofthe drawing operation, with the die in section and a portion of the tube'broken away; and Fig. 2 shows the relative positions of the tools andtubing after the drawing operation is started.

In the usual commercial methods of drawing tubing, metal is initiallyformed into a hollow cylindrical blank which is subsequently reduced indiameter and gauge by successive passes through drawing dies havingtapered or conical apertures progressively decreasing in diameter to thedesired external diameter of the tube. During the drawing operation theinterior of the tube is in contact with a mandrel corresponding to thedesired interior diameter of the tube, and positioned interiorly of thedrawing die. The mandrel may be of uniform diameter and of a lengthequal to the length of the tubing, or may take the form of a bulb fixedto the end of a long rod. In the latter case, the rod is anchored at oneend of the drawing bench and is of a length sufficient to position theenlarged portion or bulb within the aperture of the drawing die duringthe drawing operation.

The customary method of operation with this type of mechanism is tofirst swage or collapse one end of the tube to be drawn to a size whichwill permit its entry into the draw die aperture. The bulb or mandrel isthen threaded into the opposite end of the tube until the endof themandrel or bulb is substantially in contact with the swaged end, whichis then inserted in the die aperture. If a mandrel having a uniformdiameter throughout its length is used, the tubconnecing is usuallypushed through the die by some suitable mechanism operating on theopposite end of the mandrel, and if a, bulb mandrel is used, the swagedend is gripped by suitable gripping means and the tubing is pulledthrough the die.

By utilizing the type of mechanism illustrated in the attached drawing,the laborious threading operation may be eliminated. In this form ofmechanism, we provide a loose or unattached mandrel or bulb I formed toprovide a bearing surface 2 having a diameter equal to the desiredinside diameter of the tubing 3. The die 4 is provided with an aperturehaving a bearing surface 5, of a diameter substantially equal to thedesired outside diameter of the tubing, and a flared entry surface 6,substantially as shown. The enlarged portion of the mandrel I has adiameter greater than the diameter of. the bearing surface 5 of the die,to insure that the mandrel will not be drawn through the die during thedrawing operation.

' In the drawing operation, the mandrel is placed in the end of the tubea short distance from its end, and the end of the tube is swaged down,as shown, or otherwise reduced, to a diameter which will permit of itsinsertion in the die. The end of the tube is gripped by means of thetongs 8, which are then actuated by a draw ing bench mechanism, notshown, to pull the tube through the die and over the mandrel I up intoposition within the die illustrated in Fig. 2 To insure that the mandreli will be brought into its proper position in the die, the tube 3 isprovided with an indentation 9 near the position of the end of themandrel away from the swaged 'end of the tube. This indentation willforce the mandrel into the die aperture and will subse quently beeffaced as the drawing operation proceeds.

If the exterior surface of the mandrel conforms closely with theconfiguration of the flared surface 601. the die, it has been found thatupon attempting to draw a tube, the friction between the tube and thesurfaces of the mandrel and die is usually too great. As a result, thetube is not reduced in diameter and gauge as intended, but becomeswedged tightly in the drawing tools and generally breaks under thetensile force applied to effect the drawing operation. However, if themandrel is so shaped as to provide contact with the tube over only aportion of its length, the friction may be reduced to an extent whichpermits the drawing operation to be successfully performed. Thisreduction of contact area is suitably effected by forming the mandrelwith a relieved area ill. The entering tubing is thus in contact withthe enlarged portion of the mandrel as indicated at H and the surface 6of the die, and is reduced to gauge upon passing through the openingdefined by the mandrel surface 2 and the die surface 5.

Due to the swaging operation and the gripping action of the tongs,particularly when drawing light gauge and small diameter material, theend of the tube is virtually sealed. If the mandrel i is solid, it isapparent that upon pulling the tubing through the die a vacuum will beset up in the space 12 bounded by the tube wall, the swaged end of thetube, and the one face of the mandrel. It has been found that the vacuumcaused by this drawing operation results in the production of tubinghaving a diameter less than that which would be produced by the sametools if air were allowed ingress into the space l2, and may result inthe production of material which varies in diameter along its length.This latter eifect obtains when the seal formed by the swaged end is notperfect and some air leaks through the swaged end, relieving the vacuumfrom time to time. These fluctuations of the air pressure withinthe tubeare reflected by corresponding variations in the diameter of the tubingproduced. If the tubing is of extremely thin gauge, the pressurediiferential at high drawing speeds is sometimes suflicient to cause apartial collapse of the tube wall, produced longitudinally extendingwrinkles in the tube.

The vacuum thus formed could be relieved, of course, by puncturing thetube at a point between the swaged end and the die, but this results ina substantial weakening of the tubes resistance to the tensile stressesoccasioned by the drawing operation. It has been found preferable toprovide an opening l3 through the bulb to eliminate the differentialpressure.

In addition to performing this function, the opening IS in the bulbserves another purpose. It is necessary, in cold drawing operations, tokeep the surfaces of the tubing well lubricated where they pass throughthe die or over the bulb. When the tubing is of relatively largeinternal diameter, it is not difflcult to get oil or other lubricatingmaterial into the interior of the tube so as to cover the entireinterior surface, but in smaller diameter tubing, the lubricant can beintroduced only by pressure. If the mandrel is solid and the tube pulledthrough the die, the lubricant will be wiped out by the drawingoperation, but when the mandrel is provided, as shown, with a relativelysmall diameter hole extending through its length, the lubricant will bewiped back until it reaches a level above the opening in the mandrel.The difference between atmospheric pressure and the pressure occurringin the space l2 causes the lubricant to flow through the opening in themandrel, depositing the lubricant on the interior surface of the tubewhich has already passed through the die, thus lubricating the interiorof .the tube for a succeeding drawing operation.

What is claimed is:

1. The method of drawing tubing which includes positioning a loosemandrel inwardly from the end of a tube, swaging the tube end, insertingthe swaged end in a drawing die having a flared entry surface; indentingthe tube at a point inwardly from the end. of the 'mandrel opposite theswaged end ofthe tube, gripping the end of the tube and pulling saidtube through said die until a portion of the mandrel adapted to definethe internal diameter of the tube is in cooperative relationship with aportion of the die adapted to define the periphery of the tube, stoppingthe further entry of the mandrel into the die opening by contact of a.limited area of an enlarged portion of said mandrel with the tube withinthe flared entry of the die, and continuing to draw the tube around themandrel and through the die while relieving the vacuum formed betweenthe gripped end of the tube and the mandrel by an aperture extendingthrough said mandrel.

2. The method of drawing tubing which includes positioning a loosemandrel inwardly from the end of a tube, swaging the tube end untilsubstantially sealed to the passage of air therethrough, inserting theswaged end in a drawing die, indenting the tube at a point past the endof the mandrel farthest removed from the swaged end of the tube,gripping the swaged end of the tube, pulling said tube and mandrelthroughsaid die until a portion of the mandrel adapted to define theinternal diameter of the tube is in cooperative relationship with aportion of the die adapted to define the external diameter of the tube,arresting the entry of themandrel into the die opening, continuing todraw the tube over the mandrel and through the die, and utilizing theair pressure differential existing on opposite sides of said mandrel toforce lubricant into the portion of the tube reduced by the drawingoperation through an aperture extending through said mandrel.

3. The method of drawing tubing which includes positioning a loosemandrel inwardly from the end of a tube, swaging the tube end, insertingthe swaged end in a drawing die having a flared entry surface, grippingthe end of the tube and pulling said tube and mandrel through said dieuntil a portion of the mandrel adapted to define the internal diameterof the tube is in cooperative relationship with a portion of the dieadapted to define the external diameter of the tube,

the die opening by contact of a limited area of an enlarged portion ofsaid mandrel with the tube within the flared entry of the die, andcontinuing to draw the tube over the mandrel and through the die whilerelieving the vacuum formed between the gripped end of the tube and themandrel by .an aperture extending through said mandrel.

4. The method of drawing tubing which includes positioning a loosemandrel inwardly from the end of a tube, swaging the tube end, insertingthe swaged end in a drawing die, gripping the end of the tube andthereby sealing the tube against the ingress of air through the swagedend,

pulling said tube through said die until a portion of the mandreladapted to deflne the internal diameter of the tube is in cooperativerelationship with a portion of the die adapted to define the peripheryof the tube, arresting the movement of the mandrel into the die opening,continuing to draw the tube over the mandrel and through the die, andutilizing the air pressure differential existing on opposite sides ofsaid mandrel to force lubricant into the portion of,

the tube reduced by the drawing operation through an aperture extendingthrough said mandrel.

CHARLES MILLER HERE, Administrator of the Estate of Theodore Moore,

Deceased. I

GEORGE E. NIGHIHART.

- preventing the further entry of the mandrel into

